.TH "subasync" 3 "Sat Aug 16 2025 14:15:23" "Paho MQTT C Client Library" \" -*- nroff -*-
.ad l
.nh
.SH NAME
subasync \- Asynchronous subscription example 
.PP

.PP
.nf
#include <stdio\&.h>
#include <stdlib\&.h>
#include <string\&.h>
#include "MQTTClient\&.h"

#define ADDRESS     "tcp://test\&.mosquitto\&.org:1883"
#define CLIENTID    "ExampleClientSub"
#define TOPIC       "MQTT Examples"
#define PAYLOAD     "Hello World!"
#define QOS         1
#define TIMEOUT     10000L

volatile MQTTClient_deliveryToken deliveredtoken;

void delivered(void *context, MQTTClient_deliveryToken dt)
{
    printf("Message with token value %d delivery confirmed\\n", dt);
    deliveredtoken = dt;
}

int msgarrvd(void *context, char *topicName, int topicLen, MQTTClient_message *message)
{
    printf("Message arrived\\n");
    printf("     topic: %s\\n", topicName);
    printf("   message: %\&.*s\\n", message\->payloadlen, (char*)message\->payload);
    MQTTClient_freeMessage(&message);
    MQTTClient_free(topicName);
    return 1;
}

void connlost(void *context, char *cause)
{
    printf("\\nConnection lost\\n");
    printf("     cause: %s\\n", cause);
}

int main(int argc, char* argv[])
{
    MQTTClient client;
    MQTTClient_connectOptions conn_opts = MQTTClient_connectOptions_initializer;
    int rc;

    if ((rc = MQTTClient_create(&client, ADDRESS, CLIENTID,
        MQTTCLIENT_PERSISTENCE_NONE, NULL)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to create client, return code %d\\n", rc);
        rc = EXIT_FAILURE;
        goto exit;
    }

    if ((rc = MQTTClient_setCallbacks(client, NULL, connlost, msgarrvd, delivered)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to set callbacks, return code %d\\n", rc);
        rc = EXIT_FAILURE;
        goto destroy_exit;
    }

    conn_opts\&.keepAliveInterval = 20;
    conn_opts\&.cleansession = 1;
    if ((rc = MQTTClient_connect(client, &conn_opts)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to connect, return code %d\\n", rc);
        rc = EXIT_FAILURE;
        goto destroy_exit;
    }

    printf("Subscribing to topic %s\\nfor client %s using QoS%d\\n\\n"
           "Press Q<Enter> to quit\\n\\n", TOPIC, CLIENTID, QOS);
    if ((rc = MQTTClient_subscribe(client, TOPIC, QOS)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to subscribe, return code %d\\n", rc);
        rc = EXIT_FAILURE;
    }
    else
    {
        int ch;
        do
        {
                ch = getchar();
        } while (ch!='Q' && ch != 'q');

        if ((rc = MQTTClient_unsubscribe(client, TOPIC)) != MQTTCLIENT_SUCCESS)
        {
                printf("Failed to unsubscribe, return code %d\\n", rc);
                rc = EXIT_FAILURE;
        }
    }

    if ((rc = MQTTClient_disconnect(client, 10000)) != MQTTCLIENT_SUCCESS)
    {
        printf("Failed to disconnect, return code %d\\n", rc);
        rc = EXIT_FAILURE;
    }
destroy_exit:
    MQTTClient_destroy(&client);
exit:
    return rc;
}

.fi
.PP
 
